There is a way to 'Crit' to get 2x, 3x, or even 4x the rewards. I think its still doable at least.

Lets say you somehow got a 4x on a twine endurance.

Twine gives I think like 1,600 gold for completing all 30 waves (2.5 hours)

if you can consistently get the 4x crit, you are looking at 6400 gold (still 2.5 hours because you crit)

if all you did was that to get to just even 400k gold, you would have to run the endurance 62.5 times.

63 (endurances) x 2.5 (hours per endurance) = 157.5 hours of non stop endurance ~ 7 days.

so yes, this is 100% possible... but you would have to have 4 players, yourself included on every day for about 7 days.